Background: Taxometric and behavioral genetic studies suggest that attention deficit hyperactivity disorder (ADHD) is best modeled as a dimension rather than a category. We extended these analyses by testing for the existence of putative ADHD-related deficits in basic information processing (BIP) and inhibitory-based executive function (IB-EF) in individuals in the subclinical and full clinical ranges. Consistent with the dimensional model, we predicted that ADHD-related deficits would be expressed across the full spectrum, with the degree of deficit linearly related to the severity of the clinical presentation. Method: A total of 1547 children (aged 6-12 years) participated in the study. The Development and Well-Being Assessment (DAWBA) was used to classify children into groups according to levels of inattention and hyperactivity independently: (1) asymptomatic, (2) subthreshold minimal, (3) subthreshold moderate and (4) clinical ADHD. Neurocognitive performance was evaluated using a two-choice reaction time task (2C-RT) and a conflict control task (CCT). BIP and IB-EF measures were derived using a diffusion model (DM) for decomposition of reaction time (RT) and error data. Results: Deficient BIP was found in subjects with minimal, moderate and full ADHD defined in terms of inattention (in both tasks) and hyperactivity/impulsivity dimensions (in the 2C-RT). The size of the deficit increased in a linear manner across increasingly severe presentations of ADHD. IB-EF was unrelated to ADHD. Conclusions: Deficits in BIP operate at subclinical and clinical levels of ADHD. The linear nature of this relationship provides support for a dimensional model of ADHD in which diagnostic thresholds are defined in terms of clinical and societal burden rather than representing discrete pathophysiological states. Copyright © Cambridge University Press 2014.